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OCR for page 183
F Retorting Technologies for Oil Shale HOT GAS RETORTING PROCESSES In the Paraho internal combustion retort a moving bed of shale travels downward and is heated by hot gas flowing upward through it. The hot gas is provided by combustion of hydrocarbon gas and char within the retort. Oil produced from the pyrolysis process is carried out of the retort by the gas stream in the form of vapor and oil mist (liquid). Paraho demonstrated this process at a scale of about 300 tons/day. In the Union B and Petrosix retorts the hot gas is provided by heating the hydrocarbon gases produced by pyrolysis in an external heater. The hot gas flows countercurrent to the shale particles. In the Union B process the shale is pumped upward and the gas flows downward; in the Petrosix proc- ess the shale moves downward and the gas flows upward. Fuel from an external source is normally supplied to operate the heater. Petrosix has been operating in Brazil more or less continuously since 1972 at 2200 tons/ day (800 bbl/day) in a retort 18 ft in diameter and is constructing a 7800- ton/day (3300-bbl/day) retort with a diameter of 36 ft. Union has con- structed a plant to produce 10,000 bbl/day. Construction was finished in 1983, and oil shipments began in 1986. Work continues in an effort to increase the achieved capacity of 7000 bbl/day to design capacity. In a modified in-situ process a fixed bed retort is constructed under- ground by some combination of mining and blasting. Downward-flowing gas is heated by burning the char in the retort. Occidental Petroleum and the U.S. Department of Energy have been the most active in developing this process, demonstrating its feasibility at Logan Wash in the early 1980s. Occidental Petroleum is proposing to demonstrate its process on its Colo- rado tract, C-b, where commercial-sized mine shafts have been constructed. 183
OCR for page 183
184 APPENDIX F Rio Blanco (Gulf and Amoco) developed variations of the process in the early 1980s. Geokinetics was also active then in developing a horizontal insitu process, which avoided mining by using near-surface blasting. HOT SOLID RETORTING PROCESSES In the Tosco II process hot ceramic balls are mixed with smaller shale particles in a rotating drum. After the shale is pyrolyzed, the balls are separated and reheated in a ball heater using gas as fuel. The retorted shale is discarded. Tosco operated this process on a scale of 1000 bbl/day in the late 1970s and early 1980s. In the Lurgi process hot burned shale is rapidly mixed with raw shale in a screw mixer and then held in a surge bin for a few minutes to complete pyrolysis. After pyrolysis the shale is fed to a lift pipe (dilute fluid bed), where it is burned as it is pneumatically lifted in a stream of air. The hot burned shale exiting from the lift pipe provides a continuous source of hot solid. Rio Blanco (Gulf and Amoco) operated a 1- to 5-tons/day pilot until 1984. In the Chevron process raw shale and hot burned shale are mixed in a staged fluidized bed and held there until pyrolysis is complete. A lift pipe is used to burn the retorted shale and provide hot solid, as in the Lurgi process. Chevron constructed and briefly operated a 350-tons/day pilot plant until 1984. In the Lawrence Liverm ore National Laboratory (LLNL), hot solids proc- ess mixing of recycled hot shale with raw shale occurs in a few tens of seconds in a fluidized bed. Pyrolysis is completed in a few minutes as the hot shale particles flow through a bin. The char is burned to produce hot solid in a cascading burner. Solid particles cascade down through a series of rods that slow their fall and provide sufficient residence time for com- bustion. Oxygen is provided by air flowing across the tumbling solid par- ticles. The LLNL has operated a laboratory-scale retort at 1 ton/day, which is currently being enlarged to 4 tons/day.